# # 原始列表
nums = [5, 12, 7, 9, 21, 7, 14]
# 统计数字7出现的次数
count_seven = nums.count(7)
print("数字7出现的次数:", count_seven )
# 判断99是否存在,不存在则添加
if 99 not in nums:
nums.append(99)
print("添加99后的列表:",nums )
# 删除第一次出现的数字7
nums.remove(7) # 只删除第一个7
print("删除第一个7后的列表:", nums)
# 取出第2个到第4个元素(索引1到3)
sub_list = nums [1:4]
print("第2~4个元素组成的列表:", )
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数字7出现的次数: 2
添加99后的列表: [5, 12, 7, 9, 21, 7, 14, 99]
删除第一个7后的列表: [5, 12, 9, 21, 7, 14, 99]
第2~4个元素组成的列表: